Conventional implant constructions are generally of a two-part design and include a body portion which is adapted to be recessed into the patient's jaw, and a prosthesis in the form of a ceramic tooth which is adapted for coupling to a proximal end of the body. The implantable body which is made from stainless steel, titanium or other suitable metals or alloys is configured to be recessed into a suitable bore hole formed in the patient's jaw bone at the site of a lost tooth. Typically, the body has a threaded interior or is otherwise configured to mechanically receive thereto an attachment post which serves as a support for the ceramic tooth.
U.S. Pat. No. 5,344,457 to Pilliar et al., entitled “Porous Surfaced Implant”, discloses a frustoconical shaped implant which is characterized by a porous coated bone engaging lower portion and a smooth non-porous upper bone attachment region or collar. The implant is press-fitted into a complementary sized bore formed in the patient's jaw bone at the site of placement and over time, bone tissues grow into and engage the porous coating on the lower portion of the implant to firmly anchor it in the place of a natural tooth. The implant which is the subject of U.S. Pat. No. 5,344,457 has achieved a significant degree of success in the market place, and is presently sold by Innova Corp. of Toronto, Canada, under the name Endopore®. Endopore® dental implants are used in the replacement of various teeth including, lost molars and bicuspid teeth in the anterior and posterior regions of the mouth.
Other conventional implant constructions are characterized by the implantable body being cylindrical in shape and provided with a roughened lower exterior surface, texture, external thread configuration and/or coating, to facilitate the engagement of the implant body with the patient's surrounding bone tissues and its anchoring in place.
A difficultly exists with conventional implants in that todate, they have achieved limited success in replacing incisors and teeth in the frontal-most regions of the mouth where high aesthetic demands exist. The abutment-implant interface, also termed “microgap”, is believed to harbor bacteria and bacterial products following exposure to the oral environment. This in turn results in the establishment of a “biological width” around the implant (i.e. the distance from the peri-implant bone crest to the microgap). The biological width is relatively constant and seems to be approximately 2 mm, similar to the biological width present around natural teeth. It has been found that following implantation, crestal bone remodeling occurs, whereby supporting bone tissues and the overlying bone tissues tend to recede to the uppermost peripheral edge of the textured or porous coated bone engaging portion of the implant body. A further variable that can play a role in crestal bone remodeling is lack of mechanical coupling around any smooth upper collar surface. For example, it has been demonstrated that the crestal bone resorption around Endopore® implants stops at the junction of the smooth collar and the porous surface. It has been suggested that the lack of mechanical coupling around the smooth collar surface results in “disuse atrophy” of the crestal bone to the level of the junction with the porous surface. This has been demonstrated also with other textured implant surfaces.
The receding supporting tissues or crestal bone loss around dental implants has led to an aesthetic challenge when attempting dental restorations in that it may result in exposure of the metal implant body, greatly detracting from the natural appearance of the prosthesis. Conventional implants suffer the disadvantage in that the alveolar bone which encases the tooth root tends to gradually disappear along the portion of the implant where engagement of bone tissue with the implant body does not occur. This leads to a corresponding recession of the sulcus and overlying gum tissues which gradually results in the exposure of the silver/grey stainless or titanium steel body of the implant. In the more aesthetically important regions of the mouth, the exposure of the stainless steel portion of the implant body may be seen through the patient's gum tissue as a grey tinted band, greatly detracting from the natural look of the prosthesis.
This problem is particularly pronounced in the anterior regions of the mouth and when using two implants positioned adjacent to each other. Loss of inter-implant bone height (as a result of the normal crestal bone remodeling that is associated with each of the implants) results in the absence of a papilla between the two implants due to lack of bone support. This creates an aesthetic deformity, often termed “black triangle”, between the two implant crowns. “Black triangles” are particularly visible when present in the maxillary anterior region and the patient has a high lip line. The patient's perception of a successful implant-supported prosthesis depends not only on restoring function, but also on restoring normal anatomy and aesthetics. The lack of a papilla and the presence of a “black triangle” can lead to patients' dissatisfaction with the whole implant treatment, even with patients having a low smile line. Heretofore, the dental profession has been forced to come up with techniques to deal with “black triangles”. Most commonly, pink acrylic or porcelain is added to the final restoration to replace the missing papilla. This solution is far from ideal since it is impossible to replicate the gingival tissue with acrylic or porcelain in terms of texture and colour. Several attempts have also been made in establishing surgical procedures that will regenerate the missing papilla; however, these procedures are very unpredictable and seldom result in 100% regeneration.
Conventional implants are poorly suited to accommodate for the crestal bone remodeling which occurs with implants. With conventional implant designs, most often any bone engaging textured, porous or coated surface extends downwardly from an uppermost radial edge surface which is located a constant distance from the lower apex of the body. Conventional implant designs suffer the disadvantage that they fail to account for the fact that with natural incisor teeth, the surface contour of healthy supporting bone tissues tends to be higher along the distal and medial surfaces of the tooth than along the lingual and buccal regions. Heretofore, the bone engaging regions for conventional implants have either been limited by the lowermost extent of expected bone recovery, weakening the integrity of the dental implant attachment, or suffer the disadvantage that the lingual and buccal portions of the implantable portion of the implant body may be visible at the patient's gum line.